<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{margin: 0;padding: 0;}
        ul{list-style: none;}
        #menu{width: 100px;height: 30px;margin: 20px auto;border: 1px solid red;position: relative;}
        #menu ul{width: 100px;border: 1px solid black;position: absolute;top: 30px;left: -1px;display: none;}
        #menu:hover ul{display: block;}
        #menu ul li:hover{background: lightgreen;}
    </style>
</head>
<body>
    <div id="menu">
        卖家中心
        <ul>
            <li>列表项1</li>
            <li>列表项2</li>
            <li>列表项3</li>
            <li>列表项4</li>
        </ul>
    </div>
</body>
</html>